1. Field of the Invention
The present invention relates to a nonreciprocal circuit device such as a circulator and an isolator for use in a microwave band.
2. Description of the Related Art
Generally, lumped element isolators used in portable communication apparatuses such as cellular phones allow signals to pass only in the transmission direction, and inhibit transmission in the opposite direction. The recent trend toward lighter and smaller portable communication apparatuses has increased the demand for lighter and smaller isolators.
In order to meet such demands, Japanese Unexamined Utility Model Application Publication No. 5-80009 discloses a nonreciprocal circuit device including wound-wire center electrodes formed by winding center electrode conductors around a magnetic body to reduce the size and weight of the device. The center electrodes of this nonreciprocal circuit device have greater effective lengths to improve the inductance of the center electrodes and to reduce the diameter of the magnetic body.
However, the center electrodes are formed by winding the center electrode conductors around the magnetic body with the nonmagnetic substrate that is left at the bottom of the magnetic body for reinforcement when the thickness of the magnetic body is thin. Since the portions of the wound center electrode conductors at the bottom of the magnetic body are separated from the corresponding portion of the magnetic body by the nonmagnetic substrate, the insertion loss of the resulting isolator is not sufficiently low as required for isolators.
To overcome the above-described problems, preferred embodiments of the present invention provide a nonreciprocal circuit device including a magnetic body provided with a nonmagnetic substrate, that achieves miniaturization, weight reduction, and low insertion loss.
A preferred embodiment of the present invention provides a nonreciprocal circuit device including a center electrode including a nonmagnetic substrate including a first surface having a groove, a magnetic body provided on a second surface of the nonmagnetic substrate, and a center electrode conductor, a portion of the center electrode conductor being arranged in the groove, and a magnet for applying a direct-current magnetic field to the magnetic body, the magnet being disposed in proximity to the magnetic body.
Since the nonmagnetic substrate is provided with the groove and has a reduced thickness at the groove, the distance between the center electrode conductor and the magnetic body is greatly reduced as compared with the case where no groove is provided. Thus, the insertion loss greatly decreased. Moreover, since the depth of the groove in the nonmagnetic substrate can be controlled, the insertion loss is easily controlled. Furthermore, since a portion of the center electrode conductor is provided in the groove, displacement of the center electrode is effectively prevented.
Preferably, the magnetic body includes a side of the groove, and the nonmagnetic substrate includes a base of the groove.
The depth of the groove is arranged to reach an interface between the nonmagnetic substrate and the magnetic body. Also, the magnetic body defines a base of the groove. Moreover, sides of the nonmagnetic substrate define sides of the groove.
According to this preferred embodiment of the present invention, the nonmagnetic substrate is not provided between the center electrode conductor and the magnetic body, and the thickness of the magnetic body is sufficiently maintained. Therefore, the insertion loss of structure described above is greatly reduced.
Preferably, the center electrode conductor includes a wire having an insulating coat, and the center electrode conductor is either wound around the nonmagnetic substrate and the magnetic body or only wound around the magnetic body.
When the center electrode conductor is wound around the nonmagnetic substrate and the magnetic body, the windings of the conductor are not in direct contact with one another at the intersections of the windings since the conductor is provided with an insulating coat.
The magnetic body preferably includes a magnetic garnet single crystal so as to further reduce the insertion loss.
The magnetic body is preferably grown by liquid phase epitaxy. In this manner, the magnetic body has the same crystal structure as that of the substrate and has high crystallinity. Thus, a high-quality nonreciprocal circuit device having a low insertion loss is manufactured using this magnetic body.
The nonmagnetic substrate preferably includes a garnet single crystal. When both the nonmagnetic substrate and the magnetic body have the same garnet single crystal structure, a nonreciprocal circuit device having stable characteristics and low insertion loss is manufactured therefrom.
Further elements, characteristics, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.